1. Technical Field
This invention relates to a new variable resolution global map generating system for structuring digital mapping data in a new data base structure. managing and controlling the digital mapping data according to new mapping data access strategies, and displaying the mapping data in a new map projection of the earth.
2. Background Art
Numerous approaches have been forwarded to provide improved geographical maps, for example:
U.S. Pat. No. 4,315,747, issued to McBryde on Feb. 16, 1982, describes a new map "projection" and intersecting array of coordinate lines known as the "graticule", which is a composite of two previously known forms of projection. In particular, the equatorial portions of the world are represented by a fusiform equal area projection in which the meridian curves, if extended, would meet at points at the respective poles, referred to as "pointed poles". In contrast, the polar regions of the world map are represented by a flat polar equal area projection in which the poles are depicted as straight horizontal lines with the meridians intersecting along its length. Thus, in a flat polar projection the meridian curves converge toward the poles but do not meet at a point and, instead, intersect a horizontal linear pole. The two component portions of the flat world map are joined where the parallels are of equal length. The composite is said to be "homolinear" because all of the meridian curves are similar curves, for example, sine, cosine or tangent curves, which merge where the two forms of projection are joined where the respective parallels are equal. The flat polar projections in the polar portions of the map provide a compromise with the Mercator cylinder projections, thereby greatly reducing distortion.
U.S. Pat. No. 1,050,596, issued to Bacon on Jan. 14, 1913, describes another composite projection for world maps and charts which uses a Mercator or cylindrical projection for the central latitudes of the earth and a convergent projection at the respective poles. In the central latitudes, the grids of the Mercator projection net or graticule are rectangular. In the polar regions, the converging meridians may be either straight or curved.
U.S. Pat. No. 1,620,413, issued to Balch on Dec. 14, 1926, discusses gnomic projections from a conformal sphere to a tangent plane and Mercator or cylindrical projections from the conformal sphere to a tangent cylinder. Balch is concerned with taking into account the non-spherical shape of the earth, and therefore, devises the so-called "conformal sphere" which represents the coordinates from the earth whose shape is actually that of a spheroid or ellipsoid of revolution, without material distortion.
U.S. Pat. No. 752,957, issued to Colas on Feb. 23, 1904, describes a map projection in which a map of the entire world is plotted or transcribed on an oval constructed from two adjacent side by side circles with arcs joining the two circles. The meridians are smooth curves equally spaced at the equator, while the latitude lines are non-parallel curves.
U.S. Pat. No. 400,642 issued to Beaumont on Apr. 2, 1889, describes a map of the earth on two intersecting spheres, on which the coordinate lines of latitude and longitude are all arcs of circles.
U.S. Pat. No. 751,226, issued to Grinten on Feb. 2, 1904, represents the whole world upon the plane surface of a single circle with twice the diameter of the corresponding globe, the circle being delineated by a graticule of coordinates of latitude and longitude which are also arcs of circles.
U.S. Pat. No. 3,248,806, issued to Schrader on May 3, 1966, discloses a subdivision of the earth into a system of pivotally mounted flat maps, each map segment representing only a portion of the earth's surface in spherical projection on an equilateral spherical triangle to minimize distortion.
U.S. Pat. No. 2,094,543, issued to Lackey et al on Sept. 28, 1937, describes a projector for optically producing a variety of different map projections, including orthographic, stereographic and globular projections onto flat translucent screens and a variety of other projections on shaped screens.
U.S. Pat. No. 2,650,517, issued to Falk on Sept. 1, 1953, describes a photographic method for making geographical maps.
U.S. Pat. No. 2,354,785, issued to Rohl on Aug. 1, 1944, discloses two circular maps which are mounted side by side, and an arrangement for rotating the two maps in unison so that corresponding portions of the earth's surface are at all times in proper relationship.
U.S. Pat. No. 3,724,079, issued to Jasperson et al on Apr. 3, 1973, discloses a navigational chart display device which is adapted to display a portion of a map and enable a pilot to fix his position, to plot courses and to measure distances.
U.S. Pat. No. 2,431,847 issued to Van Dusen on Dec. 2, 1947, discloses a projection arrangement, in which a portion of the surface of a spherical or curved map may be projected in exact scale and in exact proportional relationship.
McBryde and Thomas, Equal Area Projections for World Statistical Maps, Special Publication No. 245, Coast & Geodetic Survey 1949.
In addition to the above further teachings as to geographical mapping can be found in the Elements of Cartooraphy, 4th edition which was written by Arthur Robinson, Randall Sale and Joel Morrison, and published by John Wiley & Sons (1978).
The present invention seeks to provide a low cost and efficient mapping system which allows the quick and easy manipulation of and access to an extraordinary amount of mapping information, i.e., a mapping system which allows a user to quickly and easily access a detailed map of any geographical area of the world.
Map information can be stored using at least three different approaches, i.e., paper, analog storage and digital storage, each approach having its own advantages and disadvantages as detailed below.
The paper mapping approach has been around since papyrus and will probably exist for the next thousand years.
Advantages of paper storage:
inexpensive.
once printed, no further processing is required to access the map information, so not subject to processing breakdown.
Disadvantages of paper storage:
can become bulky and unwieldy when dealing with a large geographical area, or a large amount of maps.
paper does not have the processing capabilities or "intelligence" of computers, and therefore does not support automated search or data processing capabilities.
cannot be updated cheaply and easily.
The analog mapping approach is used to provide what is commonly known as videodisc maps. The information is stored as still frames under N.T.S.C. (National Television Standards Committee) conventions. To make maps, a television camera moves across a paper map lying on a workbench. Every few inches a frame is recorded on videotape. After one row of the map is completely recorded, the camera is moved down to the next row of frames to be recorded. This process is repeated until frames representing a checkerboard pattern of the entire map are recorded. The recorded videotape could be used to view the map: however, access time to scan to different areas of the recorded map is usually excessive. As a result, a videodisc, with its quicker access time, is typically used as the medium for analog map storage. The recorded videotape is sent to a production house which "stamps" out 8 inch or 12 inch diameter, videodiscs.
Advantages of the analog storage approach:
one side of a 12 inch videodisc can hold 54.000 "frames" of a paper map. A frame is typically equal to 21/2.times.3 inches of the paper map.
access time to any frame can be fast usually under 5 seconds.
once located on the videodisc, the recorded analog map information will be used to control the raster scan of a monitor and to produce a reproduction of the map in 1/30th of a second.
through additional hardware and software, mapping symbols, text and/or patterhsn can be overlaid on top of the recorded frame.
Disadvantages of the analog storage approach:
the "frames" are photographed from paper maps, which, as mentioned above, cannot be updated cheaply or easily.
due to paper map projections, mechanical camera movements, lens distortions and analog recording electronics, the videodisc image which is reproduced is not as accurate as the original paper map.
as a result of the immediately above phenomena, latitude and longitude information which is extracted from the reproduced image cannot be fully trusted.
if a major error is made in recording any one of the 54,000 frames, it usually requires redoing and re-stamping.
since frames cannot be scrolled, most implementations employ a 50% overlap technique. This allows the viewer to jump around the database with a degree of visual continuity: however, this is at a sacrifice of storage capacity. If the frame originally covered 21/2.times.3 inches or approximately 8 square inches of the paper map, the redundant overlap information is 6 square inches, leaving only 2 square inches of new information in the centroid of each frame.
as a result of the immediately above deficiency, a 2.times.3 foot map containing 864 square inches would require 432 frames; thus, only 125 paper maps could be stored on one side of a 12 inch videodisc.
must take hundreds of video screen dumps to make a hard copy of a map area of interest and, even then, the screens do not immediately splice together because of the overlap areas.
the biggest disadvantage is that, since frames have to be arranged in a checkerboard fashion, there is no way to jump in directions other that north, south, east or west and maintain visual continuity. As an example, the visual discontinuity in viewing a "great circle" route from Alaska to New York would be unbearable for all but the most hearty.
The digital mapping approach has been around for at least 20 years and is much more frequently used than the analog approach. Digital data bases are stored in computers in a format similar to text of other databases. Unlike map information on a videodisc, the outstanding map features are stored as a list of objects to be drawn, each object being defined by a plurality of vector "dot" coordinates which define the crude outline of the object. As one example, a road is drawn by connecting a series of dots which were chosen to define the path (i.e., the "outline") of the road. Once drawn, further data and processing can be used to smooth the crude outline of the object, place text, such as the name or description of the object in a manner similar to what happens when drawing on a paper map.
Advantages of the digital approach:
digital maps are the purest form of geographical mapping data: from them, paper and analog maps can be produced.
digital maps can be quickly and easily updated in near real-time, and this updating can be in response to data input from external sources (e.g., geographical monitoring devices such as satellite photography).
digital maps can be easily modified to effect desirable mapping treatments such as uncluttering, enhancing, coloring, etc.
digital maps can be easily and accurately scaled, rotated and drawn at any perspective view point.
digital maps can be caused to reproduce maps in 3-D.
digital maps can drive pen-plotters (for easy paper reproductions), robots, etc.
digital maps can be stored on any mass storage device.
Disadvantages of the digital approach:
digital maps require the use or creation of a digital database: this is a very time-consuming and expensive process, but once it is made, the data base can be very easily copied and used for many different projects.
The digital approach is utilized with the present invention, as this approach provides overwhelming advantages over the above-described paper and analog approaches.
In designing any mapping system, several features are highly desirable:
First, it is highly desirable that the mapping system be of low cost.
Second, and probably most important, is access time. Not only is it generally desirable that the desired map section be accessible and displayed within a reasonable amount of time, but in some instances, this access time is critical.
In addition to the above, the present invention (as mentioned above), seeks to provide a third important feature,--a mapping system which allows the manipulation of and access to an extraordinary amount of mapping information, i.e., a mapping system which allows a user to quickly and easily access a detailed map of any geographical area of the world.
A tremendous barrier is encountered in any attempt to provide this third feature. In utilizing the digital approach to map a large geographical area in detail (e.g., the earth), one should be able to appreciate that the storage of mapping data sufficient to accurately define all the geographical features would represent a tremendous data base.
While there have been digital mapping implementations which have successfully been able to manipulate a tremendous data base, these implementations involve tremendous cost (i.e., for the operation and maintenance of massive mainframe computer and data storage facilities). Furthermore, there is much room for improvement in terms of access time as these mainframe implementations result in access times which are only as quick as 20 seconds. Thus, there still exists a need for a low-cost digital mapping system which can allow the storage, manipulation and quick (i.e., "real time") access and visual display of a desired map section from a tremendous mapping data base.
There are several additional mapping system features which are attractive.
It is highly desirable that a mapping system be sensitive to and compensate for distortions caused by mapping curved geographical (i.e., earth) surfaces onto a flat, two-dimensional representation. While prior art approaches have provided numerous methods with varying degrees of success, there is a need for further improvements which are particularly applicable to the digital mapping system of the present invention.
It is additionally attractive for a mapping system to easily allow a user to change his/her "relative viewing position", and that in changing this relative position, the change in the map display should reflect a feeling of continuity. Note that the "relative viewing position should be able to be changed in a number of different ways. First, the mapping system should allow a user to selectively cause the map display to scroll or "fly" along the geographical map to view a different (i.e., "lateral") position of the geographical map while maintaining the same degree of resolution as the starting position. Second, the mapping system should allow a user to selectively vary the size of the geographical area being displayed (i.e., "zoom") while still maintaining an appropriate degree of resolution, i.e., allow a user to selectively zoom to a higher "relative viewing position" to view a larger geographical area with lower resolution regarding geographical, political and cultural characteristics, or zoom to a lower "relative viewing position" to view a smaller geographical area with higher resolution. (Note that maintaining the appropriate amount of resolution is important to avoid map displays which are effectively barren or are cluttered with geographical, political and cultural features.) Again, while prior art approaches have provided numerous methods with varying degrees of success, there is a need for further improvements which are particularly applicable to the digital mapping system of the present invention.
The final feature concerns compatibility with existing mapping formats. As mentioned above, the creation of a digital database is a very tedious, time-consuming and expensive process. Tremendous bodies of mapping data are available from many important mapping authorities, for example, the U.S. Geological Survey (USGS), Defense Mapping Agency (DMA), National Aeronautics and Space Administration (NASA), etc. In terms of both being able to easily utilize the mapping data produced by these agencies, and represent an attractive mapping system to these mapping agencies, it would be highly desirable for a mapping system to be compatible with all of the mapping formats used by these respective agencies. Prior art mapping systems have been deficient in this regard; hence, there still exists a need for such a mapping system.